A read channel integrated circuit is a component in a hard disk drive. For example, in a magnetic recording system, a read channel converts and encodes data to enable the magnetic recording heads to write data to the disk drive and then read back the data accurately. The disks in a drive have many tracks on them and each track may include user or “read” data sectors as well as control or “servo” data sectors. The information recorded in the servo sectors helps to position the magnetic recording head on track so that the information stored in the read sectors is retrieved properly.
At the beginning of a read or servo event (i.e., when the read or servo sector is being read), the read channel may perform a zero gain start (ZGS) to quickly predict the gain error in the readback signal prior to acquisition of the readback signal's gain and timing. However, current ZGS designs use the zero-forcing (ZF) algorithm in nature. ZF algorithm does not consider noises and therefore performs differently in different noise environment. Therefore, the current ZGS designs have a bias up to several dB when the least mean square (LMS) algorithm is used in gain loop acquisition/tracking. More specifically, at high signal-to-noise ratio (SNR), ZF and LMS have similar performances; however, at a lower SNR, ZF has worse performance than LMS, and the performance difference results in the ZGS bias. Such a bias therefore presents a challenge for using ZGS in real applications.
Therein lies the need to provide a method and system for estimating and mitigating the ZGS bias.